Signature of rapid and large atmospheric pressure variations inabsolute and relative gravity measurements

Since 1996, gravity variations have been measured at J9 Observatory near Strasbourg (France), with both an absolute FG5 gravimeter designed by Micro-g Lacoste and a superconducting gravimeter designed by GWR. Other parameters, such as the temperature, air pressure, humidity and level of the water table have also been continuously measured since 1996. Raw gravity data are corrected for atmospheric pressure, tidal and polar motion effects. Between 2004 and 2009, we have recorded 76 sessions of simultaneous measurements of both the FG5 and superconducting gravimeters. The duration of an observation ranges from 24 hours up to one week. For 9 simultaneous measurements, we have detected significant anomalous variations of absolute gravity which can be approximated by a linear trend. These variations are not, however, detected in the data provided by the superconducting gravimeter. We can safely dismiss any mishandling of the FG5 by the operator. Instead, the occurrence of anomalous gravity variations is correlated to rapid and large pressure variations due to abrupt changes in the weather conditions